The prior art has provided diaphragm valves to selectively allow and prevent passage of a flowing fluid. In one type of diaphragm valve a housing is provided with a chamber having an outlet opening, an inlet passageway communicating between the chamber and the outside of the housing for receiving the flowing fluid within the chamber and an outlet passageway communicating between the outlet opening and the outside of the housing for discharging the flowing fluid from the chamber and out of the housing. The housing is also provided with a projection extending into the chamber and having an annular sealing surface surrounding and sloping away from the outlet opening to form a valve seat. Additionally, a valve body is located within the chamber that has a recess and elastomeric diaphragm covering the recess. The valve body is adapted for movement towards and away from the valve seat between a closed position and an open position. In the closed position, the diaphragm is flexed into the recess by the projection, conformingly and sealably contacting the sealing surface and covering the outlet opening, to prevent the passage of the flowing fluid through the housing. In the open position, the diaphragm is spaced from the valve seat and the outlet opening is uncovered to allow the passage of the flowing fluid through the housing.
The problem with a diaphragm valve incorporating an elastomeric diaphragm is that the elastomeric material forming the diaphragm may chemically react with certain fluids. Such a chemical reaction may introduce impurities, i.e. chemical products from the reaction and fine particles of elastomer, into the flow of the fluid. As a result, diaphragm valves incorporating elastomeric diaphragms are not suitable in applications where the purity of the fluid is to be maintained.
In another type of prior art diaphragm valve design, the diaphragm is fabricated from a metal that is not chemically reactive with the flowing fluid so that the diaphragm valve may be used in high purity applications. An example of such a valve design may be found in U.S. Pat. No. 4,828,219. In the valve design of this patent, a chamber defined in a housing is subdivided by a metal diaphragm into a pair of valve and drive chambers. The fluid flows into the valve chamber through an inlet passageway and out of the valve chamber through an outlet opening of an outlet passageway. A valve seat, provided within the valve chamber surrounds the outlet opening. A valve stem, located within the drive chamber, is forceably driven against the diaphragm to in turn drive the diaphragm against the valve seat in order to seal the outlet opening and thereby to prevent passage of the flowing fluid through the valve housing.
In order to effectuate a seal in a metal diaphragm valve, such as that disclosed in U.S. Pat. No. 4,828,219, relatively high valve closing forces are required. For instance, in one embodiment of the '219 patent, a handle is provided to urge the stem against the diaphragm. The high closure force of the '219 patent makes the valve design, disclosed therein, particularly unsuitable for applications requiring rapid valve actuation and/or light valve closure forces. In the prior art, rapid valve actuation is produced by electromagnetic actuation and such electromagnetic actuation does not produce enough force to close the valve of the '219 patent. In a diaphragm valve design having an elastomeric diaphragm, such as discussed above, relatively low valve closure forces are required because only light forces are required to deform the elastomer into its deformed state sealing the outlet opening. In order to produce a metal diaphragm valve having a rapid actuation time and a light valve closing force, it is not possible to simply replace the elastomeric diaphragm in the elastomeric diaphragm valve with a metal diaphragm. If this were done, when the metal diaphragm contacted the valve seat, it would flex or crease over the valve seat and therefore, no seal would be produced between the valve seat and the diaphragm. If one attempted to increase the valve closure force to prevent creasing, a permanent deformation would be produced in the diaphragm to prevent valve resealing.